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one degree deeper than he wore for common purposes in the day time- and the Author uses No. 2 in ordinary, but at Night sees many faint Stars well with No. 3, which he cannot see at all with No. 2. This is especially remarkable in the early part of the Evening when the Stars first become visible. And at Large Theatres, he finds one Number deeper than that which he ordinarily uses is a very advantageous indulgence to his Eye.
To give more assistance to the Sight to see a distant object, many persons hold a Concave Eye-Glass very obliquely to the Eye-in which position, a Concave No. 3 will give almost the same sharpness of outline to objects as No. 34 when held parallel to the Eye.
FOR DISTANT OBJECTS, extremely Shortsighted persons should use A SMALL OPERAGLASS, which having an adjustable focus, if it
able to Newton's remark, and consequently nearer the retina of a short-sighted person; but the parts of the retina surrounding the circle of dissipation of a star being in the dark, the fainter colours, blue, indigo, and violet, will have some share in forming the image, and consequently the focus will be shorter."-See Phil. Trans. Vol. LXXIX.
only magnifies Twice, will be infinitely better than any single Concave, because it can be exactly adapted to various distances.
My "Invisible Opera-Glass," a contrivance of Mr. PIERCE and myself, is a great acquisition to Short-sighted Persons, and is an inestimable little Instrument for Artists, &c. who wish to discern the distinct outline of objects at short inaccessible distances; i.e. for an Architect to see the exact outline of a Building a furlong off- or to examine the pointing, &c. of the walls of upper stories, &c.
When shut up in its case, this little Glass is only 2 inches in length; — when in use, about 3 inches: it has a single plano-convex Objectglass of an inch in diameter, and its Magnifying power is about 3 times.
* An Opera-Glass which only magnifies once, like the fashionable Grand Dandy Operas - of which the Eye-glass is as large as the Object-glass-is of no use to a Nearsighted person;-who, to receive the same benefit which a common Eye does, will require rather more magnifying power: A very short-sighted person will receive very little more assistance from an Opera-glass which magnifies Twice, than a person with a Common Eye will from one which magnifies Once.
There is a very general Vulgar Error, that Short-sighted persons who use Concaves, as they get older, become less Short-sighted: on the contrary, every Optician and Short-sighted person that I have consulted on this subject, have assured me, that as their Eyes become impaired by Age, to see distant objects sharp and distinct, they require rather deeper than shallower Concaves; and at a very advanced Age, sometimes complain that they cannot see to read so well as formerly, and require Converes of 36 or 30 inches focus.
Mr. PIERCE informs me, that Dr. PARKER, the late Rector of St. James's, Piccadilly, had from his youth a short-sight, and when almost four score years of age, complained to him that he could not read so distinctly as he wished: with the help of Convexes of 36 inches focus, he was enabled to read and write with comfort to himself for several Years after. - See Appendix.
That a Short-sight is stronger and better, and more lasting than a Common-sight — I have always set down among the most absurd of Vulgar Errors- unless, to be half blind all their Life, as the Short-sighted are, is better
than to be so only during about one-third of it, and that during the latter part of Life, as common Eyes are.
This prejudice is as foolish as the silly notion some people have - that a severe fit of Gout, is a thing to give a man Joy of — which our philosophical poet, Pope, admirably illustrated when he said:
"So when small humours gather to a Gout,
Essay on Man.
If the observations of Lord Chesterfield and Dr. Reid are true, a Short-sighted Person without Spectacles, is under a sad disadvantage in the common business of Life. The following
is the advice this keen observer of Human
Nature gave to his Son:
"Mind not only What people say,— but How they say it: if you have any sagacity, you may discover more truth by your Eyes than by your Ears. People can Say what they will, but they cannot Look just as they will; and their Looks frequently discover what their Words are calculated to conceal."- See Letter 77.
Dr. THOS. REID's observation on the Eye is" Of the faculties called the Five Senses," Sight is, without doubt, the noblest: by means thereof we can perceive the tempers and dispositions, the passions and affections of our fellow-creatures, even when most they want to conceal them: and when the Tongue is taught most artfully to lie and dissemble, the Hypocrisy appears in the countenance to a discerning Eye! and we can perceive what is straight and what is crooked in the Mind, as well as in the Body."- Inquiry into the Human Mind, 8vo. 1818, p. 140.
However, it is some consolation to the Shortsighted, to consider, that if the natural infirmity of their Eyes prevents their enjoying this advantage, the use of Spectacles not only enables them to see what is passing in the Eyes of others, but that they form a veil over their own, which, in a great degree, prevents any such Scrutiny; and thus their Weakness becomes their Strength.